1. Field of the Invention
The present invention relates to an apparatus and method for detecting a rotation angle of a rotating body, and in particular, to a learning technique for improving detection accuracy.
2. Description of the Related Art
In Japanese Unexamined Patent Publication No. 9-133039, a technique for improving detection accuracy in a low throttle opening range is disclosed in which a signal from a throttle sensor (rotation angle sensor) that detects a throttle opening of an internal combustion engine, is directly input to a first A/D converter, and the sensor signal is amplified a predetermined number of times and input to a second A/D converter, and the amplified signal via the second A/D converter is used when the throttle opening is low, and the signal via the first A/D converter is used when the throttle opening is high.
Moreover, in the disclosed technique, in order to solve a problem where, when an amplification ratio of the amplifier differs from a calculated value, the throttle opening detection values vary and become discontinuous on the low opening side and the high opening side of a switching point of the output values of the respective A/D converters, the point of discontinuation can be resolved by finding the ratio of the output values for a predetermined opening, and correcting the amplification ratio according to this ratio.
However, in the above correction of the amplification, while variation in the amplifier can be learnt, variation in the sensor itself cannot be absorbed.
Furthermore, as shown in FIG. 2 of the above-mentioned Publication, since the amplified signal becomes saturated at an intermediate opening, there has been a problem in that a conversion characteristic (gain) between the sensor output and the rotation angle cannot be learnt.